He’s not the first to leave Fratton Park to join up with his former manager. We’ve had a look at what happened to all 28 permanent signings Cook made during his time in PO4.
1. Michael Doyle (signed from Sheffield United)
Doyle returned to former club Coventry in 2017, having captained the Blues in their League Two-winning season. The next season he captained the Sky Blues to League One promotion before joining Notts County in January. | Freelance Photo: Colin Farmery
2. Gareth Evans (signed from Fleetwood Town)
The former Manchester United trainee signed in July 2015 and has gone on to become a Pompey hero. A key member of the Blues' 2016/17 promotion campaign, last season he scored 10 league goals to help the club reach the play-offs. | JPIMedia Photo: Joe Pepler
3. Enda Stevens (signed from Aston Villa)
Stevens arrived at Pompey having played for the Republic of Ireland under-21s, and in the Europa League for Shamrock Rovers. In 2017 he joined Sheffield United, and will play at left-back for them in next season's Premier League. | JPIMedia Photo: Joe Pepler
4. Adam Barton (signed from Coventry City)
Barton left Pompey after only a season, signing for Partick Thistle. He was named the club's player of the year in his first season but joined Dundee United after relegation in 2018. Last month he joined Wrexham. | Other 3rd Party Photo: SCC