Whelpdale told BBC Radio Cambridgeshire: "It's been quite surreal really.
"I suppose it's been a bit of a surprise, but definitely a good surprise as we got on well before."
Ferguson returned to London Road on Wednesday just 14 months after leaving the club by mutual consent.
Whelpdale, who played a key role as Posh won promotion from League One under Ferguson in 2009, switched from right-wing to right-back for Saturday's 3-1 defeat by Brighton, with Mark Little dropping to the bench.
Posh currently have the worst defensive record in the Football League and Whelpdale said he was eager to establish himself as a first choice defender.
"I enjoy playing right back because I'm still able to get forward and attack," he continued. "I played their a lot under Darren Ferguson last time around."
Source: BBC Sport
Source: BBC Sport