Nico Rosberg says it is "virtually impossible" to have a close relationship with Lewis Hamilton due to their Formula One rivalry within the Mercedes team.
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The pair enjoyed a close friendship when coming through the motorsport ranks, with both men having driven karts in their formative years.
Since coming together as team-mates at Mercedes in 2013 their friendship has become somewhat strained, though, as they have battled it out for the Formula One drivers' title.
Hamilton won back-to-back titles in 2014 and 2015, but could not prevent Rosberg winning a maiden championship this season.
Following the season finale in Abu Dhabi, Hamilton appeared not to make eye contact or shake Rosberg's hands until they were on the podium.
Rosberg admits that their personal dynamic has changed considerably, but he remains a big fan of the Briton's driving ability.
"Lewis is one of the best of all time. He sets a high standard," the 31-year-old told a media conference during a visit to his Wiesbaden birthplace in Germany.
"It will always be difficult between us. We are in the same team and race against each other for titles. It is virtually impossible to have a good relationship.
"We used to be best friends when we were young so at least we have this respect for each other. This helps somewhat.
"I do not know how he feels at the moment but I know how I felt in 2014 and 2015. For me it was difficult to stomach. In 2015 I lost to him again. It will now take some time for him to process this."