The 23-year-old was formerly on the books at Crystal Palace, who sold him to Lyon for just six figures last year, and the Irishman immediately made a name for himself in France.
O'Brien came up with an impressive five goals and two assists in 32 matches for Lyon across all competitions, as Les Gones enjoyed a remarkable revival in the second half of the season, finishing sixth to sneak into the Europa Conference League.
However, Lyon must cope without the 23-year-old for their latest continental adventure, as Everton announced the £16.4m signing of O'Brien on a four-year deal on Tuesday.
"I'm buzzing and so happy to have signed for Everton. I've been dreaming of this kind of move in the Premier League, with such a historic club. It's a very exciting move for me," O'Brien told the official Everton website.
O'Brien's arrival at Goodison Park has relit the fire surrounding the future of Jarrad Branthwaite, who was heavily linked with a move to Manchester United before the Red Devils signed Leny Yoro from Lille.
West Ham United 'make decision' on Danny Ings future
At the other end of the field - and the other end of the country - West Ham United have reportedly decided not to try to force Danny Ings out of the door this summer.
The former Liverpool striker has failed to make the grade at the London Stadium since leaving Aston Villa midway through the 2022-23 season, scoring a paltry four goals in 52 matches.
Ings was on target just once in 30 games across all competitions last season, where Michail Antonio and Jarrod Bowen were often preferred in the central attacking spot under David Moyes.
New manager Julen Lopetegui is also thought to be keen to bring in a new striker, but according to Football Insider, the Irons are not actively trying to rid themselves of Ings.
Lopetegui supposedly feels that the 32-year-old can still offer something to the Hammers in the 2024-25 season, and he is likely to continue at the London Stadium even if West Ham strike a deal for Aston Villa's Jhon Duran.
Ings is now in the last year of his £120,000-a-week West Ham contract, and he is allegedly unwilling to lower his salary in order to leave, meaning that he is likely to depart for nothing in 2025.
Anwar El Ghazi 'pushing' to return to English football
Sticking with the theme of former Aston Villa flames, Dutch attacker Anwar El Ghazi is reportedly making a concerted effort to return to English football with Championship side Cardiff City.
The 29-year-old is currently a free agent after an acrimonious end to his time with German side Mainz 05, whom he joined last summer but made just three Bundesliga appearances for.
El Ghazi and Mainz severed ties just six weeks after his arrival due to the winger's pro-Palestine social media post, and it was ruled earlier this month that the German side wrongfully dismissed him.
According to Sky Sports News, El Ghazi - who is owed more than £1m in unpaid wages and bonuses from Mainz thanks to the court's ruling - is now pushing to join Cardiff on a free transfer.
Once El Ghazi receives his compensation from Mainz, the ex-Aston Villa man is expected to seal his switch to the Cardiff City Stadium, marking his return to England two years after leaving Aston Villa.
El Ghazi previously made 73 Premier League appearances across his spells at Everton and Villa, while he has also represented Ajax, Lille and PSV Eindhoven in his well-travelled career.
Aberdeen 'reject' £3m Espanyol bid for striker
Finally, Aberdeen have reportedly knocked back an offer from Spanish outfit Espanyol for striker Bojan Miovski.
The North Macedonia international has enjoyed two prolific seasons at Pittodrie since joining from MTK Budapest in 2022, notching 44 goals in 96 appearances across all tournaments.
Miovski is now in the last two years of his agreement, though, and according to the Daily Mail, Espanyol recently tried their luck with an offer of £3m for the 25-year-old.
However, the Scottish side immediately rejected the proposal and are said to be holding out for a fee of £6.5m to sell Miovski, who is also in contact with Genoa and Bologna of Serie A.
A £3m transfer would have still represented a significant profit on the £548,300 that Aberdeen paid to bring the striker to the club two years ago, but the club are determined to make him their record sale.
That honour is currently held by right-back Calvin Ramsay, who was sold to Liverpool for £4.4m in 2022.